It may be held either up or down (5)
I believe the answer is:
tenet
This clue is a double definition.
'it may be held' is the first definition.
(idea or belief someone might hold)
'either up or down' is the second definition.
(Other definitions for tenet that I've seen before include "you may believe in it" , "Key principle" , "Fundamental belief" , "A religious doctrine proclaimed as true without proof" , "Item of belief" .)